I recently ran into a post that had this to say about an observation. I know that sudden changes in CO2 and lighting can be hard on plants, but what typically causes crypt melt?
I was giving that warning about CO2, crypts and very low light because I have never seen it mentioned anywhere else. I have seen it happen twice, and the second time I kept the CO2 high after the crypts started melting, and the melting continued day after day until most of the leaves were gone. My observation conflicts with articles by Ole Pedersen and others in The Aquatic Gardener that say that CO2 fertilization is nothing but good at all light levels. That may be true for the majority of aquarium plants, but I am convinced that these crypts (wendtii and cordata) are an exception.